Science : The alarm clock that rings every spring

WHEN temperatures drop and food becomes scarce, many small mammals go into hibernation to survive the winter. Now researchers in California have located part of the timing mechanism that tells animals when to sleep and when to wake up. It lies within the hypothalamus, a region of the brain that controls sleep, sex and temperature regulation.

By maintaining their body temperatures at only a degree or so above that of the air outside, hibernating mammals such as dormice can dramatically reduce the energy they expend. During hibernation they remain in a death-like sleep for days at a time. Just as most animals have a body clock that induces a daily rhythm of activity, hibernating mammals seem to have one set on an annual cycle.

Irving Zucker of the University of California at Berkeley and colleagues from Stanford University noted that a small part of the hypothalamus called the suprachiasmatic nucleus ...

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